Limited diffraction feedback laser system having a composite sensor

ABSTRACT

A low diffraction-feedback high-energy laser system includes an injection laser, a master oscillator power amplifier (MOPA), and means for aligning the injection laser to the MOPA. A composite sensor for providing a dual-sensing capability is disclosed including a mosaic array and a superposed quad sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention is related to three co-pending applications filed on evendate herewith, respectively entitled LIMITED DIFFRACTION FEEDBACK LASERSYSTEM, LIMITED DIFFRACTION FEEDBACK LASER SYSTEM HAVING A CONTROLLEDDISTORTION CAVITY-FEEDBACK MIRROR, and LIMITED DIFFRACTION FEEDBACKLASER SYSTEM HAVING A CAVITY TURBULENCE MONITOR, each of the sameassignee as herein and respectively invented by William M. Johnson,William M. Johnson, and William M. Johnson et al, each incorporated byreference.

FIELD OF THE INVENTION

This invention is directed to the field of optics, and moreparticularly, to a novel limited diffraction feedback laser systemhaving a composite sensor, controlled distortion cavity-feedback mirrorand cavity turbulence monitor.

BACKGROUND OF THE INVENTION

In many applications including directed energy weapons systems, it isdesirable to both transmit outgoing pulses of high energy laser lightand to receive reflected return energy from a target during theinterpulse intervals along the same but reciprocal optical path. Suchsystems are called upon to separate the outgoing and received opticalenergies along a common optical aperture, to detect the relativemis-alignment therebetween, and to correct the relative misalignmentbetween the outgoing and received optical energies to maintainsubsequent pulses both on-target and in-focus.

One impediment to the utility of such systems is thermal loading. As theoutgoing laser energy is produced, it is partly absorbed as heat by thecavity mirrors of the optically active cavity. The mirrors thermallyexpand, changing their figure, which therewith throws the outgoing laserpulses out of focus. In addition, both the phenomena of edge diffractionoff of the cavity mirrors and that of intracavity turbulence tend tobreak up the high energy laser beam formation process. Such systems arethus further called upon to provide an outgoing beam of high energylaser light in a manner that is substantially free of the undesirableeffects of cavity mirror thermal loading, intracavity turbulence, andcavity diffraction-feedback.

SUMMARY OF THE INVENTION

The high-energy laser system of the present invention includes a primaryconcave reflector and a spaced secondary convex reflector having acommon focus and defining therebetween an optical oscillation andamplification cavity. The primary and secondary reflectors each includea central aperture therethrough, and the secondary reflector is sized tobe slightly larger than, or the same size as, the hole in the primaryreflector. An injection laser is coupled to the optical oscillation andamplification cavity through the hole in the primary reflector. An arrayof injection laser sensors and cooperative relay mirrors are providedintermediate the injection laser and the optical oscillation andamplification cavity for aligning the injection laser vis-a-vis the axisof the optical oscillation and amplification cavity. The injection laserand oscillation and amplification cavity cooperate with the relativesizes of the apertured convex reflector and of the apertured concavereflector to minimize diffraction-feedback and therewith to prevent thebreaking up of the high power beam.

A specular member sized to be at least as large as the hole of theconvex secondary reflector is provided behind the secondary reflector.The specular member includes a central hole therethrough, and a sensoris positioned therebehind. The injection laser is incident on the sensorbehind the hole in the specular member of the convex secondaryreflector, and the sensor provides a signal in real-time representativeof intracavity turbulence. The injection laser energy is deviated off ofthe specular member and onto the back of the convex secondary reflector.Both surfaces thereof are thereby uniformly thermally loaded, and insuch a way as to preserve the figure of the secondary cavity mirror andtherewith the focal condition of the outgoing high-energy beam.

Means including an alignment laser and a common optical aperture laserseparator are cooperative with a composite sensor to provide outgoingand return energy alignment in real-time and to provide injection laseralignment with the optical axis of the cavity. The composite sensorpreferably includes a mosaic array sensor and a superposed quad cellsensor. In one embodiment, the laser separator is provided internally ofthe cavity. In a further embodiment, it is positioned externally of thecavity. In both embodiments, the composite sensor provides both a cavityboresighting and an injection laser alignment function.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and attendant advantages of the presentinvention will become apparent as the invention becomes betterunderstood by referring to the following solely exemplary andnon-limiting detailed description of the preferred embodiments thereof,and to the drawings, wherein:

FIG. 1 is a schematic diagram illustrating one embodiment of the limiteddiffraction feedback laser system having a composite sensor, controlleddistortion cavity-feedback mirror and cavity turbulence monitoraccording to the present invention;

FIG. 2 is a schematic diagram illustrating another embodiment of thelimited diffraction feedback laser system having a composite sensor,controlled distortion cavity-feedback mirror and cavity turbulencemonitor according to the present invention;

FIG. 3 illustrates in FIG. 3A a pictorial diagram, and illustrates inFIG. 3B a fragmentary and enlarged pictorial diagram, of a controlleddistortion cavity-feedback mirror of the limited diffraction feedbacklaser system having a composite sensor, controlled distortioncavity-feedback mirror and cavity turbulence monitor according to thepresent invention; and

FIG. 4 illustrates in FIGS. 4A and 4B plan diagrams illustrating acomposite sensor of the limited diffraction feedback laser system havinga composite sensor, controlled distortion cavity-feedback mirror andcavity turbulence monitor according to the present invention andillustrates in FIGS. 4C and 4D partial schematic diagrams illustratingthe composite sensor as hard-wired in FIG. 4C and as utilizingpreselected pixels of the mosaic array to provide the quadcell functionin FIG. 4D according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, generally designated at 10 is a schematicdiagram illustrating one embodiment of the novel limited diffractionfeedback laser system having a composite sensor, controlled distortioncavity-feedback mirror and cavity turbulence monitor according to thepresent invention. The system 10 includes a primary concave reflector 12and a spaced-apart controlled distortion secondary reflector assemblygenerally designated 13 to be described. The assembly 13 includes aconvex secondary reflector 14 that defines with the primary reflector 12an optical oscillation and amplification cavity therebetween that isgenerally designated at 16. The primary reflector 12 and the secondaryreflector 14 each have a radius of curvature and a focal point, and areso spaced-apart that their focal points are coincident. The radii ofcurvature of the reflectors 12, 14, and their diameters, are selected inwell-known manner to provide an intended cavity magnification factor.The reflector 12, 14 are preferably spherical segments, although otherconical segments can also be employed, and are preferably fabricatedentirely of any suitable metal capable of accepting and retaining such ahigh degree of polish as to provide a specular surface.

The primary concave reflector 12 has a central aperture therethroughgenerally designated 18. The secondary reflector 14 is preferablydimensioned to be slightly larger than, or of the same size as, thecentral aperture 18 of the primary reflector 12, and it includes acentral aperture generally designated 20 therethrough that is in theshadow of the aperture 18 of the primary reflector 12. The aperture sizeand alignment prevent optical cavity energy from feeding back into theinjection laser cavity. A 45° scrapper mirror 22 preferably is providedaround the secondary reflector 14. Light pulses that walk-out of thecavity 16 in well-known manner are deviated off the scrapper mirror 22through optics generally designated 24 and onto a targeted object, notshown. Return energy present along the same but reciprocal optical pathduring the interpulse intervals of the outgoing light pulses aredeviated through the optics 24 and the mirror 22 into the cavity 16.

A laser separator generally designated 26 is provided intermediate theprimary and secondary reflectors 12, 14 for separating outgoing andreturn optical energy along a common optical aperture. The laserseparator 26 preferably includes a metallic disk 28 having polishedspecular surfaces 30, 32 that is mounted for rotation with the shaft ofa motor 34. The disk 28 includes at least two apertures generallydesignated 36 therethrough. As the disk 28 rotates, the apertures 36thereof are aligned with the axis of the cavity 16 for some angularorientations of the disk 28, and at other angular orientations thereof,the reflecting surfaces 30, 32 are aligned with the axis of the cavity16.

Reference may be had to co-pending U.S. utility patent application Ser.No. 512,153, now U.S. Pat. No. 4,684,796, entitled COMMON OPTICALAPERTURE LASER SEPARATOR FOR A RECIPROCAL PATH OPTICAL SYSTEM, inventedby William M. Johnson and assigned to the same assignee as the instantinvention, incorporated herein by reference, for a further descriptionof the laser separator.

An alignment laser 35 and a confronting extended corner cube reflector38 are provided transverse the axis of the cavity 16 and to either sideof the disk 28. The alignment laser may be any suitable cw or pulsedlaser device. A beam splitter 42 is positioned along the path of thealignment laser 35 to deviate light present therealong onto a compositesensor generally designated 44 to be described.

An injection laser 46 designated "IL" having spaced cavity mirrorsschematically illustrated in dashed lines 48 is coupled to the cavity 16via a laser amplifier 50 designated "AMP" and relay mirrors 52, 54positioned in spaced relation along the optical path of the injectionlaser. The injection laser 46 is coupled to the synchronizer 40, and itpreferably is pulsed, although a cw laser can be employed. Two degree offreedom x, y tilt actuators 56, 58 respectively are mounted to the backsof the relay mirrors 52, 54 for controlling their azimuthal andelevational pointing direction. A beam splitter 60 is providedintermediate the relay mirror 54 and the primary reflector 12 and alongthe axis of the cavity 16. A plurality of injection laser centeringsensors schematically illustrated generally at 62 to be described areprovided to maintain the injection laser beam aligned with the aperture18 of the primary reflector 12 so that it enters the cavity 16 along thecavity axis.

Referring now to FIG. 2, generally designated at 70 is anotherembodiment of the limited diffraction feedback laser system havingcomposite sensor, controlled distortion cavity-feedback mirror andcavity turbulence monitor according to the present invention. The system70 as in the embodiment of FIG. 1 includes the primary reflector 12having the central aperture 18, and the secondary reflector 14 havingthe central aperture 20 defining therebetween the optical oscillationand amplification cavity 16. The 45° scrapper mirror 22 is preferablydisposed around the secondary reflector 16. The beam control optics 24,the relay mirrors 52, 54 with associated tilt actuators 56, 58, the beamsplitter 60, the centering sensors 62, the injection laser 46 having thecavity mirrors 48, and the laser amplifier 50 are common to the FIGS. 1and 2 embodiments.

The embodiment of FIG. 2 differs from the embodiment of FIG. 1principally in the location of the common optical aperture laserseparator 26, and in the manner and mode of operation of the overalllaser system. In the embodiemtn of FIG. 2, the laser separator 26 ispositioned exteriorly of the optical oscillation and amplificationcavity 16 and behind the primary concave cavity reflector 12. Themagnification of the cavity 16 is such that the placement of the laserseparator exteriorly of the cavity 16 allows the selection of a smallerand faster spinning disk 28 and the provision of a correspondinglyhigher bandwidth response. Imaging optics 72 are positioned on theoptical path defined between the reflecting surface 30 of the spinningmetallic disk 28 and the composite sensor 44. An extended corner cubereflector 74 is provided on the optical path defined between thereflecting surface 32 of the spinning disk 28 and the composite sensor44. A synchronizer 78 responsive to the angular orientation of thespinning disk 28 is coupled to the injection laser 46.

Referring now to FIG. 3A, generally designated at 13 is an enlargedschematic view illustrating the controlled-distortion cavity-feedbackmirror assembly of the limited diffraction feedback laser systemaccording to the present invention. The secondary cavity reflectorassembly 13 includes the convex mirror 14 having the central aperture 20therethrough. The convex reflector 14 is preferably fabricated of metal,and the surface thereof confronting the injection laser, schematicallyillustrated by parallel rays 82, is highly polished to provide aspecular surface. The back surface 84 thereof preferably is coated witha black or other heat absorbing film.

A member 86 sized to be at least as large as the size of the aperture 20of the convex reflector 14 is positioned in spaced relation to theabsorbing surface 84 of the convex reflector 14. The member 86 has aspecular surface 87, and has a central aperture generally designated 88therethrough aligned with and in the shadow of the aperture 20 of themirror 14 (FIGS. 1, 2). A quad sensor 90 is positioned within theopening 88 to receive injection laser energy that passes through theapertures 20, 88 (FIGS. 1, 2). The specular member 86 is preferablyfabricated of solid metal. The reflectivity of the specular members 86,14, the absorbtivity of the surface 84, and the dimensions of theapertures 20, 88 are selected to provide an intended heat distributionon the front and back surfaces of the member 14 in response to incidentcavity energy. Preferably, the amount of heat absorbed by the frontspecular surface is selected to be equal to the amount of heat absorbedby the back surface 84 so that the convex secondary cavity mirror 14substantially uniformly changes in dimension in response to thermalloading, and thereby maintains its figure undistorted as illustratedgenerally at 92 in FIG. 3B.

The specular members 14, 86 and the quad cell 90 preferably are mountedto a housing 96. The housing preferably includes apertures generallydesignated 98 therethrough. The apertures 98 allow a heat transportfluid, not shown, to flow through the housing 96 and into contact withthe back of the member 14 to further control the heat absorbitivitycharacteristic of, and therewith the thermal loading effects on, theassembly 13. Other thermal absorbtivity control means such as an axiallyvariable plunger mounted to the specular member are also possible withinthe scope of the invention.

The controlled distortion cavity mirror assembly is capable ofestablishing and maintaining an intended mirror figure useful, amongother things, to adapt the focal characteristic of the outgoinghigh-energy laser light to changing system parameters. The mirrorassembly can be spun about its axis to further control thermal effects,and reference in this connection may be had to co-pending United Statesutility patent application Ser. No. 512,172, now U.S. Pat. No.4,580,270, entitled HIGH-ENERGY LASER HAVING GYROSCOPICALLY STABILIZEDOPTICAL ELEMENTS, invented by William M. Johnson et al and assigned tothe same assignee as the instant invention, incorporated herein byreference. Reference may also be had to allowed U.S. utility patentapplication entitled MOVEMENT AND FOCUS CONTROL SYSTEM FOR A HIGH ENERGYLASER filed on even date herewith, invented by Milton B. Trageser andassigned to the same assignee as the instant invention, incorporatedherein by reference, for its disclosure, among other things, of aclosed-loop focus control system.

A x, y tilt actuator 100 is mounted to the housing 96 for controllingthe orientation of the cavity mirror 14 in elevation and in azimuth toestablish and maintain an intended pointing direction. The quad sensor90 is responsive to the position of the centroid of the injection laserenergy 82 relative to optical null to provide a signal representative ofthe turbulence in the cavity 16 FIGS. 1, 2) in real-time.

Referring now to FIG. 4, generally designated at 110, 112 respectivelyin FIGS. 4A, 4B are plan pictorial views illustrating the compositesensor of the high-energy injection laser system according to thepresent invention. The composite sensor provides a dual-functioncapability from a single sensor location. System integratability isthereby improved, and overall system design is simplified and enhanceddue to an elimination of the need for any optics and/or coordinatingcircuitry that would otherwise be required by separate and independentsensors. The composite sensor preferably includes a comparatively-largeN×N mosaic array 112 for providing a multiple-spot wide field-of-viewtracking capability to be described. A comparatively-small quad cellsensor 114 preferably is superposed on the mosaic array 112 forproviding a wide-bandwidth and narrow field-of-view nulling capabilityto be described. The quad cell sensor 114 is preferably mounted to thecenter of the mosaic array 112, as is illustrated in FIG. 4, or it canbe mounted at any other suitable location thereof. It should be notedthat although a separate quad cell sensor is preferred, as shown in FIG.4C preselected dedicated pixels of the mosaic array 112 can also beemployed as shown in FIG. 4D. A multiple wavelength capabilityconstitutes an additional advantageous feature of the composite sensorof the present invention. The mosaic array and the quad cell array caneach be operated at a selected different wavelength, for example, at thevisible and infrared portions of the spectrum.

In operation and referring now to FIGS. 1, 3A, and 4A, at timessynchronous with the axial alignment of the openings 36 of the laserseparator 26 with the axis of the cavity 16, the injection laser 46 isrepetitively operative to produce an injection laser beam. Each suchpulse is amplified in the amplifier 50 and deviated off of the relaymirrors 52, 54 through the aperture 18 of the primary concave reflector12 and into the cavity 16. The injection laser beam oscillates betweenthe cavity mirrors of, and is amplified by, the cavity 16. The number ofround-trip oscillations depend on the selected magnification factor ofthe cavity. While in the presently preferred embodiment, the parametersof the cavity are selected such that the light undergoes three (3)oscillations therein, it will be appreciated that five (5), seven (7)and nine (9) etc oscillations are possible. The amplified lightwalks-off the convex secondary reflector 14 and onto the scrapper mirror22. The mirror 22 deviates the outgoing high energy laser pulses throughthe optics 24 onto a targeted object.

The injection laser oscillates a selected small number of times in theoscillation and amplification cavity, namely the three times of thepresently preferred embodiment. With each oscillation, diffraction offof the periphery of the secondary convex mirror 14 feeds back into thegrain region of the cavity, but because of the small number ofoscillations, the diffraction effects are insufficient to break-up theformation of the outgoing high-energy beam. In addition, the physics ofthe cavity is such that the secondary cavity mirror generates anaperture stop effect in relation to the primary cavity mirror so that byselecting as above disclosed the size of the secondary cavity-feedbackmirror to be slightly larger than, or the same size as, the hole in theprimary reflector diffraction effects are thereby further minimized.

Cavity turbulence operates to deflect the injection laser beam off theaxis of the cavity. The quad sensor 90 (FIG. 3A) of the convex feedbackmirror assembly 13 (FIG. 3A) is operative in response to the position ofthe centroid of the injection laser energy relative to optical null toprovide a signal representative of the degree of cavity turbulence. Atilt control signal, not shown, responsive to the quad sensor signal isapplied to the x, y actuator 100 (FIG. 3A) to compensate the pointingdirection of the cavity mirror for high-frequency cavity turbulenceeffects just prior to the outgoing high-energy laser pulses. In thismanner, pulse-to-pulse tilt effects induced by cavity turbulence aremonitored and corrected in real-time.

The thermal load provided by the controlled distortion assembly 13preferably is balanced on the front and back surfaces of the cavitymirror 14. It therewith maintains its figure, and the outgoing pulses ofoutgoing high-energy laser light thereby remain in-focus and on-target.As will be appreciated by those skilled in the art, it is also possibleto so load the mirror assembly as to provide an intended figure useful,for example, in system focus control.

During the interpulse intervals of successive outgoing pulses ofhigh-energy laser light and synchronous with the alignment of thereflecting surfaces 30, 32 with the axis of the cavity 16, the injectionlaser light is deviated off the reflecting surface 32 of the laserseparator 26 and onto the extended corner cube reflector 38. Thereflector 38 deviates the injection laser energy onto the beam splitter42 from which a portion thereof is deviated onto the quad sensor 114 ofthe composite sensor 112 (FIG. 4A). In response to any spacialdis-locations off optical null in the position of the injection laserenergy centroid, the composite sensor 112 provides a signalrepresentative of the internal misalignment of the injection laser withthe optical axis of the cavity. An injection laser tilt control signal,not shown, responsive to the misalignment signal is applied to the x, yactuator 58 on the relay mirror 54 to maintain the injection laseraligned with the cavity axis and centered on the secondary reflector 14.

The beam splitter 60 deviates a portion of the injection laser energyonto the centering sensor array 62. The array 62 is shown in the planeof the Figure for ease of representation, but it will be appreciatedthat it is located in a plane perpendicular to the plane of the Figure.The two sensors thereof disposed about the horizontal direction of theFigure are operative to provide a signal representative of the relativeazimuthal position of the injection laser beam, and the sensors thereofdisposed about the vertical direction of the Figure are operative toprovide a signal representative of the relative elevational position ofthe injection laser 48. A control signal, now shown, responsive to thecentering array sensor signals is applied to the x, y actuator 56 of therelay mirror 52 to maintain the injection laser externally aligned withthe cavity axis and centered at the aperture 18 of the concave mirror12. In this manner, the relay mirrors 52, 54 establish and maintain thecoaxial alignment of the injection laser with the optical oscillationand amplification cavity 16.

During the interpulse intervals of successive outgoing pulses andsynchronous with the alignment of the reflecting surface 30 of theseparator 26 about the common optical aperture, return energy presentalong the same but reciprocal path of the outgoing pulses is deviated bythe scrapper mirror 22 onto the reflecting surface 30 of the spinningdisk 28. The return energy is deviated therefrom onto the beam splitter42, which deviates it onto the mosaic array 112 of the composite sensor110 producing a spot 118 (FIG. 4A) thereon representative of the returnoptical energy.

At times synchronous with the alignment of the reflecting surfaces 30,32 of the separator 26 with the optical axis of the cavity 16 and duringthe interpulse intervals of successive outgoing high-energy laser light,the beam of the alignment laser 35 is deviated off the reflectingsurface 30 onto the cavity mirror 14, and back therefrom off thereflecting surface 30 to the beam splitter 42. The splitter 42 deviatesit onto the mosaic array 112 of the composite sensor 110 producing aspot 120 thereon (FIG. 4A) representative of the pointing direction ofthe cavity mirror 14.

Another portion of the alignment laser during the interpulse intervalsis deviated off the extended corner cube reflector 38 onto thereflecting surface 32 of the laser separator 26, and from there onto theconcave primary reflector 12. It is reflected back therefrom again offthe reflecting surface 32 back through the extended corner cubereflector 38 and onto the beam splitter 42. The splitter 42 deviates thebeam onto the mosaic array 112 of the composite sensor 110 producing animage 122 (FIG. 4A) thereon representative of the pointing direction ofthe concave mirror.

The centroids and sizes of the spots 118, 120, 122 on the sensor 112represent the relative mis-alignment of the outgoing and return opticalenergy. Any suitable means responsive to the position and sizes of thecentroids of the spots 118, 120 and 122 may be employed to maintainsubsequent outgoing pulses on-target and in-focus. Reference may be hadin this connection to allowed co-pending U.S. utility patent applicationSer. No. 516,468 entitled COMMON OPTICAL APERTURE LASER BORESIGHTER FORRECIPROCAL PATH OPTICAL SYSTEMS invented by William M. Johnson et al andassigned to the same assignee of the instant invention, and the U.S.utility patent application filed on even date herewith entitled MOVEMENTAND FOCUS CONTROL SYSTEM FOR A HIGH ENERGY LASER SYSTEM, invented byMilton B. Trageser and assigned to the same assignee of the instantinvention, both incorporated herein by reference.

Referring now to FIGS. 2, 3A and 4B, the operation of the extracavitylaser separator embodiment of the limited diffraction feedback lasersystem having composite sensor, controlled distortion cavity-feedbackmirror and cavity turbulence monitor of the present invention issubstantially identical to the operation of the FIGS. 1, 3A and 4Aembodiment insofar as output high-energy laser light formation, convexsecondary reflector figure distortion control, diffraction-induced beambreakup control, real-time cavity turbulence monitoring, and injectionlaser cavity-feedback prevention are concerned. The operation of theFIGS. 2, 3A and 4B embodiment differs from the operation of the FIG. 1embodiment in two principal respects. First, boresight alignment ofoutgoing energy with return energy present along the same but reciprocaloptical path during the interpulse intervals is accomplished without theprovision of a separate alignment laser therefor.

In the embodiment of FIGS. 2, 3A, and 4B, return energy is reflected offthe optics 24 during the interpulse intervals of successive outgoingpulses of high-energy laser and is deviated off the scrapper mirror 22into the cavity 16. The return energy oscillates between the cavitymirrors 12, 14 successively converging towards the axis thereof in sucha way as to define for each round trip oscillation "n" an annular beamcollimated when illuminating the primary reflector having amagnification factor "M^(n) " and having a "telescoped" spot sizeinversely proportional to the magnification factor. The return energypasses through the aperture 18 of the concave reflector 12 and isdeviated off the reflecting surface 30 of the separator 26. Alignedoutgoing and received energy produce co-axially aligned annular beams ofdifferent magnification factor, while mis-aligned outgoing and receivedenergy produce co-axially mis-aligned annular beams of differentmagnification factor. A light extractor, not shown, positionedintermediate the surface 30 and optics 72 is provided for extracting twoor more annular beams of selected different magnification factor, whichare imaged through the optics 72 onto the mosaic array 112 of thecomposite sensor 124 (FIG. 4B) producing sensor images 126, 128representative thereof. A control signal, not shown, is responsive tothe relative mis-alignment of the spots 126, 128 to so tilt the x, yactuator 100 (FIG. 3A) of the convex reflector assembly as to maintainsubsequent outgoing pulses on-target. For a further description of thealignment process, and of the light extractor, reference may be had toco-pending U.S. utility patent application Ser. No. 640,504 entitled,now U.S. Pat. No. 4,633,479 ALIGNMENT SYSTEM FOR A CONFOCAL UNSTABLELASER SYSTEM invented by Milton B. Trageser and assigned to the sameassignee of the instant invention, incorporated herein by reference.

The manner of injection laser alignment with the optical axis of thecavity 16 is the second principal respect in which the FIG. 2 embodimentdiffers from the embodiment of FIG. 1. During the interpulse intervalsand synchronous with the times when the reflecting surface 32 of thelaser separate 26 is aligned with the axis of the cavity 16, theinjection laser is deviated off the reflecting surface 32 of thepreferably rapidly spinning disk 28 through the extended corner cubereflector 74 and onto the quad cell sensor 114 of the composite sensor124 (FIG. 4B) via the imaging optics 72 producing as spot designated 132in FIG. 4B representative thereof. The quad cell sensor 114 (FIG. 4B)provides a signal representative of the deviation of the injection laserspot off optical null. The surfaces 32, 30 of the separator 26 define acommon optical aperture for the outgoing and the injection laser light,so that the deviations off optical null are representative ofintracavity injection laser misalignment. A control signal, not shown,responsive to the quad cell sensor signal is applied to the x, yactuator 58 of the relay mirror 54 to correct for any injection lasermis-alignment. The centering sensor array 62 is cooperative with the x,y actuator 56 of the relay mirror 52 like in the embodiment of FIG. 1 tomaintain the pointing direction of the injection laser centered withinthe aperture 18 of the convex mirror 12. It should be noted that thefunction of the laser separator can be accomplished by other suitablemeans such as a beam splitting element provided the injection laserpower is suitably low. It should also be noted that the elements 26, 44,74 and associated components can be advantageously coupled at thelow-power side of the amplifier 50 as schematically illustrated by anarrow designated at 51.

It will be appreciated that many modifications of the presentlydisclosed invention will become apparent to those skilled in the artwithout departing from the scope of the appended claim.

What is claimed is:
 1. A multiple-function sensor, comprising:a firstwide field-of-view sensor sub-assembly of comparatively-large physicaldimensions having a N×N array of comparatively low-bandwidth,light-responsive elements for providing a first sensing capability,where N is an integer greater than two; a second narrow field-of-viewsensor sub-assembly of comparatively-small physical dimension having a2×2 array of comparatively high-bandwidth, light-responsive elements forproviding a second sensing capability; and means for superimposing saidsecond sensor sub-assembly onto said first sensor sub-assembly in thesame physical location.
 2. The multiple-function sensor of claim 1,wherein said first sensor is a mosaic array sensor.
 3. Themultiple-function sensor of claim 2, wherein said second sensor is aquad cell sensor.
 4. The multiple-function sensor of claim 3, whereinsaid quad sensor is hard-wired onto said mosaic array sensor.
 5. Themultiple-function sensor of claim 3, wherein preselected ones of saidmosaic array elements are dedicated to serve as the elements of saidsecond sensor.
 6. The multiple-function sensor of claim 1, wherein saidfirst and said second sensor sub-assemblies each have a preselectedwavelength response characteristic.
 7. The multiple-function sensor ofclaim 6, wherein said characteristics are selected to be different fromeach other.
 8. The multiple-function sensor of claim 1 wherein the firstsensor sub-assembly includes sufficient array elements to resolvemultiple-spots and wherein said second sensor sub-assembly elements arearranged as a quad cell array for nulling.
 9. The multi-function sensorof claim 1, wherein said first and said second sensor sub-assemblies areoperative to simultaneously view their respective fields of view.